1. Technical Field
The invention is related to relief valve assembly which can be used for vessels carrying oils or chemical products, or for chemical tanks.
2. Description of the Prior Art
Conventional types of relief valves (ie: U.S. Pat. No. 6,604,544/RE37,989/U.S. Pat. No. 5,060,688/U.S. Pat. No. 5,873,384), due to their constructional limitations, have a lifting disc and weight placed inside of their upper body. This causes low closing pressure of the valve, which, in turn, releases an excessive amount of gas and leads to environmental pollution, decrease in safety of the tank and an uneconomical result. Relief valves used for vessel release a small amount of pressure gas through the path between a disc seat assembled with upper body and pressure disc. However the gas release is not upwards in a vertical direction but sideways to a wide spread owing to the influence of ocean wind. Therefore, conventional relief valves can not guarantee the safety against fire and safety accidents.
Further, conventional relief valves, as a result of their lifting disc and standard weight being placed inside of their upper body, do not allow proper release of pressure gas. Therefore, this makes it difficult to release the gas in short time, which causes a hammering phenomenon. Cleaning and repairing the valve becomes cumbersome when the relief disc and the weight are contaminated owing to the volatile steam containing gas compound and high viscosity of solvent based foreign ingredients.
Moreover, while the relief valve is kept sealed, the relief disc, weight and stem are always exposed to released gas which increases erosion of the parts so raw materials of high erosion resistance are expensive and uneconomical. Additionally, conventional types of relief valves, when increasing or decreasing the weight, automatically requires disassembling the whole upper and lower body out of the tank. This causes poor work efficiency as it consumes long periods of work time. All of these issues present with conventional relief valves are not to be overlooked in relief valve assembly construction.
The reason for low closing pressure of conventional relief valves is that the lifting disc and weight are placed inside of the upper body so it is quite unavoidable to see the disc and weight in a floating state unnecessarily for a long time by the pressure of releasing gas while the valve is closed. In other words, since the disc and weight placed inside the upper body are not provided with sufficient atmospheric pressure, the closing pressure is naturally reduced and therefore the valve opens for a longer period of time than necessary. The releasing gas passing between the pressure disc and disc seat assembled within the upper body, without a casket-shaped housing(50) that can lead out gas upwards in a vertical direction, travels sideways to a wide spread with a top part of upper body as a start point. Thus, the possibility of safety accidents and fire is increased.
Another example of a relief valve that has been claimed to remove excessive release of pressure gas inside a tank is published in international reference No. WO 02/095275. This, relief valve has a magnet fixed in the lower part of a stem with which the lifting disc and weight are assembled, and another magnet fixed inside of the lower body. These magnets react to each other as they become closer or contact each other.
In such circumstances, pressure gas which is generated inside of the tank, increases the gap between the magnets and at the same time pushes upwards the lifting disc and weight. The gas is then released outside of the upper body into the air. The magnetic force between the magnets might work even while the pressure gas is released out into the air. Therefore, when the release pressure starts to decrease in accordance with reduction to releasing amount of gas pressure after initial release of pressure gas, the lifting disc and weight are forced to move down by magnetic force and pressure disc closes valve. These technical considerations might be worthwhile to suggest.
However, the relief valve of inter national publication No. WO 02/095275, is complicated which increases manufacturing cost and makes it difficult to handle due to its heavy weight and also does not fit for the vessel that needs weight reduction. Therefore, the relief valve is not easy for manufacturing, transporting, facilitating, and maintaining (repairing and replacing units). It is quite inconvenient in workability, and furthermore causes unreasonable trouble that in replacing magnet it is necessary to separate it from the tank even lower body which is of heavy weight.
In addition to above, relief valve in above-mentioned international publication No. WO 02/095275 also has the same problems and defects as afore-mentioned conventional type of relief valve because it's stem, lifting disc, weight, magnet in lower part of stem, magnet inside of lower body are all inside of the upper body and lower body.
The following discussion is with regard to the problems and defects of conventional types of vacuum relief valves.
Compared to the FIG. 8 of the invention, conventional types of vacuum relief valves which stably convert buoyant pressure generated inside of tank to the level of atmospheric pressure as supersaturated gas inside of tank release out into the air, is composed of screen cover(670) and screen hood(680) which are both in one unit or assembled with body(600) and cast-iron. This construction is heavy weighed, and thus quite improper for vessels, complicated in fixing construction of screen(690), difficult to manufacture, inconvenient in assembling, maintaining and repairing and expensive.
Another example of a vacuum relief valve which attempts to solve these problems and defects, compared to the FIG. 8 of the invention, has a welded ring-shaped support unit to the center of a screen(690) and a stem path through the above support unit, so the weight of the support unit is imposed on the screen(690) and hence, as per the elapse of time, screen(690) tends to droop down consequently leading to the needs for frequent replacement or repairing work that is quite inconvenient and uneconomical.
Along with this, conventional relief valves have difficulty with proper gas releasing due to flow variation of releasing gas which is caused by extra weight of assist weight when adding assist weight to standard weight. Accordingly, closure function of the disk does not work consistently all the time when using standard weight only and when using both standard weight and assist weight.